Method for adjusting the driving performance of a motor vehicle using tire sensors

ABSTRACT

Taking into account the signals of tire sensors to adjust the driving performance of a vehicle is known. For example, the signals of contact sensors can be used to indicate the forces which act on the individual vehicle tires. According to this new method, to permit a control intervention in the shortest possible real time, especially those forces are used as a control quantity which are determined by the signals from tire sensors. This means that nominal conditions of the vehicle are converted into nominal forces F i,Soll  which are compared to the actually applied forces F i,Ist . The so produced differences in forces ΔF i  are then converted by a wheel force controller ( 2 ), for example, into brake pressure variations or variations of the engine drive torque which then influence the vehicle ( 3 ) as a controlled system. Because the forces (F i,Ist ) which act on the vehicle tires are quantities describing the driving condition of the vehicle which can be determined most quickly, the reaction time of the system is extremely short, and therefore driving performance can be better controlled.

FIELD OF THE INVENTION

The present invention relates to a method of controlling the drivingperformance of a vehicle, using tire sensors to determine forces thatact on the individual vehicle wheels.

BACKGROUND OF THE INVENTION

A method of this type is disclosed in EP Patent No. 0 444 109 B1, forexample. This publication describes a method and a device fordetermining tire prints, for the conversion thereof into forces whichact on the tires and for improvement of the driving performance of thevehicle. Beside tire sensors which sense the tire contact, there areprovided still other sensors, such as sensors for sensing the wheelcircumferential speeds, the steering angle of the wheels, the positionof the wheel suspensions and the center-of-gravity acceleration. Thecontrol method discloses sensing the forces and torques which act on therespective tire by way of tire print sensors. The forces and torquesfound are used, along with the other sensor means, to control themovement of the automotive vehicle. The above publication does notdisclose which physical quantity is the actual control quantity used bythe method.

It is state of the art, for example, to perform yaw torque control wherea nominal yaw rate is compared with an actual yaw rate and, in the eventof a discrepancy of the actual yaw rate from the nominal yaw rate, thisdifference is converted into control signals for defined correctionelements. Operation of the correction elements will then cause theactual yaw rate to approach the nominal yaw rate. When, according to theabove-mentioned publication, a defined physical quantity such as therotational speed of the wheels shall be controlled selectively, it isassumed that this speed is also the control quantity. Initially, theforces which act on the wheels must be processed to calculate a nominalspeed of the wheels. Matters are similar with respect to the steeringangle or the position of the wheel suspensions of the wheels. Thesignals of the tire contact sensors are each time converted into thephysical quantity respectively being controlled in order to compare anactual vehicle performance with a nominal vehicle performance. Thisnecessitates a major expenditure in calculations because the physicalquantity underlying the control cannot be determined directly, but onlyin a complicated fashion by converting tire contact signals into tireforces and torques and by further processing them into the physicalquantity. Such a complicated processing of signals necessitates aconsiderable length of real time, thereby entailing a long reaction timeuntil control intervention. The actual physical quantities which resultat the end of such a complicated calculation are no longer relevant atthe time they are calculated: The control quantity of the method willsuffer because the control intervention which is performed with delayonly may possibly not satisfy the demands of the actual drivingsituation.

Therefore, an object of the present invention is to provide a method ofcontrolling the driving performance of a vehicle, utilizing tiresensors, which method permits a quickest possible reaction to a criticaldriving performance by way of a controlling intervention.

SUMMARY OF THE INVENTION

This object is achieved by making the forces acting on the tires thecontrol quantity of a control circuit. The principle of the presentinvention is based on the following reflection: The tire sensors permitthe simple calculation of forces and torques in longitudinal, transverseand vertical directions. Thus, calculation of these forces and torquesrequires only little time. It is therefore advisable to take especiallythese forces into account as a control quantity of the drivingperformance in order to perform a control intervention in a most directmanner.

Of course, there may be still other physical quantities which are takeninto account in the calculation of the nominal performance of thevehicles. The preset nominal value always determines in first line thedirection in which the control quantity is adjusted. Therefore, thepreset nominal value can pass a greater loop of calculating operationsand need not always be as absolutely current as is advisable for theactual value of the driving performance. The direction in which thecontrol quantity is adjusted, as time goes by, will not vary so greatlyas the actual quantity that is characteristic of the driving conditions.

Nominal forces in a longitudinal direction or also transverse direction,such as during cornering, which are determined by way of the method ofthe present invention may be converted into brake pressure variations orabsolute brake pressures, for example. In hydraulic brake systems, theymay also be converted into valve actuation periods, or currentintensities when proportional valves are used. It is also possible tovary the engine drive torque to control driven wheels with respect tonominal forces. In this arrangement, however, the forces which act onthe tires always remain the control quantity which dictates theintervention into the wheel brakes or the engine drive torque.

To determine nominal forces, the actual forces can be processed alongwith other input quantities. For the reasons mentioned hereinabove, itis of no significance with respect to the control quality that thiscalculating operation requires a longer real time.

Thus, a control method according to the present invention for yaw torquecontrol would be such that a nominal yaw torque is calculated undercertain circumstances, however, no actual yaw torque is sensed by a yawrate sensor. On the contrary, a nominal yaw torque is converted intonominal forces which would have to act on the respective vehicle tire ifthe nominal yaw torque were coincident with the actual yaw torque. Theactual forces which act on the vehicle tire will then be controlled toapproach the nominal forces.

In an electronic brake force distribution, for example, the actualforces on the front wheels can be taken into account for determining thenominal forces for the respective rear wheels.

Further input quantities which are taken into account for thedetermination of the nominal quantities could be individual wheel speedsand a vehicle reference speed, for example. These input quantities couldtypically be sensed by way of wheel sensors or by a correspondingconfiguration of the tire sensors.

The present invention will now be explained in detail by describing twoembodiments in two Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an embodiment of the present invention which isused for yaw torque control.

FIG. 2 is a view showing a possibility of applying the present inventionfor electronic brake force distribution.

DETAILED DESCRIPTION OF THE DRAWINGS

In the FIG. 1 embodiment, a torque decomposer is furnished with anominal yaw torque M_(G) which is determined in a way not shown. Thetorque decomposer 1 determines from the nominal yaw torque M_(G) forcesF_(i,soll) which must be generated by the individual vehicle tires toachieve the nominal yaw torque M_(G) indicated. From this, along withthe actually generated forces F_(i,ist), result differences in forcesΔF_(i) which are supplied to a wheel force controller 2. The wheel forcecontroller will now calculate actions, based on the differences offorces to be adjusted, which must be carried out on the individualvehicle wheels.

In a hydraulic brake system, matters could be so that differences inpressure, absolute pressures, valve actuation times or also currentintensities for proportional valves are determined. A variation of thedrive torque can be calculated from the differences in forces for drivenwheels. The so calculated actions are performed on the vehicle 3 andhave new, updated actual forces F_(i,ist) as a result.

A nominal yaw torque to be introduced into the control circuit accordingto FIG. 1 can be calculated in a conventional manner by way of customarysensor means, for example, by way of a steering angle sensor and adefined vehicle reference speed.

However, it is also possible to take into account the individual forcesF_(i,ist) on the tire measured by tire sensors, in order to determinethe nominal yaw torque M_(G).

It is essential that the sensor signals F_(i,ist) are converted directlyin the wheel force controller 2 into actions to be taken on the vehicle3. The result is a shortest possible time of calculation forintervention into the vehicle and, thus, an improved driving performancedue to the shortened reaction time in this control circuit. Thecalculation of the nominal yaw torque M_(G) may take a longer period oftime because a nominal value specification dictates in first line thedirection of the control. The illustration of the actual drivingcondition must be much more current. This is realized by the presentinvention in an ideal way.

FIG. 2 shows the possibility of performing electronic brake forcedistribution on the vehicle by way of the present invention. The purposeof electronic brake force distribution is to prevent that the rearwheels lock before the front wheels during pedal-operated braking by wayof electronic brake pressure control on the rear-axle brakes.

Apart from the actual forces F_(iv,ist) which act on the front wheels,still other input quantities are introduced into the computer, hereintermed as EBD computer 6 in short, for determining nominal forcesF_(ih,soll) to be applied to the rear-axle brakes. The input quantitiesherein include individual wheel speeds v_(i) and the vehicle referencespeed v_(ref). Instead of these signals, other signals may be used, suchas a steering angle signal, a transverse acceleration signal, or similarsignals indicative of cornering. Besides, these data about theadditional input quantities can originate from tire sensors which havean appropriate configuration.

Thus, the EBD computer 6 determines forces which shall be generated bythe rear wheels. The forces are related to the actual forces F_(ih,ist)which indeed act already on the tires of the rear wheels. The sodetermined differences in forces on the rear wheels ΔF_(ih) which are tobe adjusted are passed on to the wheel force controller 7 which, similarto the wheel force controller 2, calculates measures which must be takento adjust the differences in forces ΔF_(ih). However, the wheel forcecontroller 7, for the purpose of electronic brake force distribution,calculates only actions to be taken on the rear wheels of the vehicle 8.After these actions have been taken, new force ratios will result on theindividual vehicle tires F_(ih,ist). These force ratios are taken intoaccount for the further control.

It applies in this case, too, that the control quantity for adjusting anoptimal electronic brake force distribution is always the amount offorces that act on the rear wheels. The forces F_(i,ist) characteristicof the actual condition of the vehicle can be processed directly. Onlythe nominal value determination undergoes a greater loop which is notcritical, however, for the reasons mentioned hereinabove.

Thus, a so-called cascade controller which permits a very quickintervention into the current driving condition of the vehicle can berealized by the present invention.

What is claimed is:
 1. Method of controlling the driving performance ofa vehicle with a closed loop control circuit comprising the steps of:using tire sensors to determine forces which act on front and reartires; utilizing the forces which act on the tires as a control variableof a closed loop control circuit; producing a difference between nominalforces and actual forces which act on the tires; and adjusting thecontrol variable using the closed loop control circuit based on thedifference between the nominal forces and the actual forces which act onthe tires, wherein the closed loop control circuit converts actualforces together with other input quantities that are characteristic of acurrent driving situation into nominal forces, wherein the actual forceson the front tires are used for determining the nominal forces on therear tires.
 2. Method as claimed in claim 1, wherein the controlvariable is brake pressure.
 3. Method as claimed in claim 1, wherein thecontrol variable is a valve actuation time of a hydraulic brake. 4.Method as claimed in claim 1, wherein the control variable is anintensity for driving a proportional valve.
 5. Method as claimed inclaim 1, wherein the control variable is an engine drive torque. 6.Method as claimed in claim 1, wherein the other input quantities includeone of individual wheel circumferential speeds and a vehicle referencespeed.
 7. Method as claimed in claim 6, wherein the other inputquantities are derived from tire sensor signals.
 8. Method as claimed inclaim 1, wherein the nominal forces which act on the tires comprises ayaw torque.